The present invention relates to new bioreactive materials used in particular for implants and prostheses on man or animals in the medical, dental and veterinarian fields.
Bioreactive materials, in accordance with the present invention, means materials resulting from the fusion of mixtures of oxides or salts or any other metallic precursor, such materials being capable of reacting biochemically with living tissues and in particular with osseous tissues.
Biologically active glasses and vitroceramics have been known for many years. Compositions containing from 40 to 60% of SiO.sub.2 and B.sub.2 O.sub.3, 25% of Na.sub.2 O, 25% of CaO and a few percent of P.sub.2 O.sub.5 have been the subject of numerous experiments. In the case of such compositions, fastening to the bone is dependent upon the formation on the surface of the material of a microporous structure developing a large specific surface, for example a silica gel, protected by a layer which is rich in Ca and P ions. The selective diffusion of the sodium, calcium and phosphorous ions and the partial dissolution of the lattice of the material are the principal steps which lead to this superficial structure causing mineralization of the bone at its surface.
According to U.S. Pat. Nos. 2,301,488 and 2,243,915, materials formed from a vitreous phase and a crystalline phase such as hydroxyapatite or other compounds of the same crystalline group are based on the principle according to which the presence of hexagonal crystalline phases in the vitreous phase assists the epitaxial growth of the apatite in the material.
In accordance with the prior art the same reactive principle on the surface of the material in contact with the living tissues always leads to the formation of a medium developing a large specific surface, such as for example a silica gel.
These various materials have an osteogenic property when they are in contact with a physiological medium. Nevertheless, experiments conducted on sheep, the results of which are given in J. of Biomedic. Mater. Res., Vol. 12, 57-65 (1978), have shown that the superficial structure developed by conventional materials do not provide long-term mechanical holding for the implants they coat. In a corrosive medium, such as the physiological medium, this superficial structure destroys itself and causes too much corrosion of the implant.